Experiments were conducted in an environmentally controlled growth chamber
to determine the effects of temperature (10/5 or 21/7 C, day/night), soil m
oisture (7, 14, or 20%), timing (preemergence [PRE] or postemergence [POST]
), and rate (9 or 18 g ai ha(-1)) of application on MON 37500 efficacy on B
romus secalinus L. and toxicity to Triticum aestivum L. MON 37500 reduced B
, secalinus plant density an average of 40% but did not reduce T. aestivum
density. PRE treatments reduced B. secalinus density 40% compared to 12% wi
th POST applications when plants were grown at 10/5 C. Soil moisture level
also influenced plant density, with 7.9 planes per pot when soil moisture w
as maintained at 7%, compared to 8.5 plants per pot with 14 or 20% soil moi
sture. MON 37500 reduced B, secalinus dry weight more at 18 g ha(-1) than a
t the 9-g ha(-1) rate when grown at 21/7 C, but no rate response occurred a
t 10/5 C. PRE applications of MON 37500 at 10/5 C decreased B. secalinus dr
y weight 22% more than PRE applications at 21/7 C or POST applications unde
r either temperature regime. However, PRE applications of MON 37500 at 21/7
C decreased T. aestivum biomass an average of 16%, compared to 3% or less
with other treatments. At 21/7 C, B. secalinus dry weight decreased 46% as
soil moisture increased from 7 to 20%. Bromus secalinus was 10 to 12% less
susceptible to MON 37500 when grown at 7% soil moisture at 10/5 C than when
grown at the same temperature at 14 or 20% soil moisture. Triticum aestivu
m injury was greater at 20% soil moisture under each temperature regime.